Antenna array



July 7, 1959 Filed NOV. '1, 1957 CRQSS REFERENCE N. Y ARU ANTENNA ARRAYEARS RGGM 2 Sheets-Sheet 1 //1 iA/70 Ma /0.44.: KMW,

N. YARU ANTENNA ARRAY July 7, 1959 Filed Nov. 1, 1957 44/51 7942 A mmuxMM,

2 Sheets-Sheet 2 United States Patent ANTENNA ARRAY Nicholas Yaru, SantaMonica, Calif., assignor to Hughes Aircraft Company, Culver City,Calif., a corporation of Delaware Application November 1, 1957, SerialNo. 695,185

'11 Claims. (Cl. 343-77 1) This invention relates to electromagneticwave antennas and particularly to a reverse end-fire waveguide array.

Directive electromagnetic wave beams have been produced extensively byutilizing arrays such as wave conductors and associated radiators. Theseradiators may be suitably spaced along the wave conductor and driven byelectromagnetic wave energy with appropriate relative amplitudes andphases. The most common configuration of arrays are radiators such asslots, probes or dipoles coupled directly to a waveguide. Such arraysare one-dimensional and often termed linear arrays.

Linear arrays in which a plurality of radiators are electromagneticallycoupled to a waveguide are usually designated as either end-fire arraysor broadside arrays. Endfire arrays produce a beam directed along theaxis of the array whereas the broadside array produces a beam whosemaximum intensity has a direction normal to the axis of the array.End-fire arrays have become very useful where the cross-section of theantenna is to be kept at a minimum. Small mechanical cross-sections areimportant to reduce aerodynamic drag when the antenna is mounted upon amobilized vehicle. Small electrical cross-sections are important toreduce radar detection. This invention is particularly suitable forend-fire arrays.

Two types of end-fire linear arrays are employed, one type being theordinary or forward end-fire array and the other type being the reverseend-fire array. In the ordinary end-fire array the main lobe or beamlies along the array axis and has the same direction as the wave energyflow within the array waveguide. In the reverse end-fire arrays the mainbeam also lies along the array axis but has a direction exactly oppositeto that of the wave energy flowing within the array waveguide.

The theories and techniques for feeding an array of radiators coupled toa waveguide to obtain the conventional forward end-fire pattern are wellknown in the art. See, for example, Microwave Antenna Theory and Design,by Silver, volume 12, of the MIT Radiation Laboratory Series, chapter 9,page 257. The design of these end-fire linear arrays is relativelysimple because the phase relation required between adjacent radiators iseasily realizable without loading the waveguide to decrease the velocityof propagation. The phase excitation of each radiator must lag that ofthe preceding radiator in order to radiate a beam along the axis of thearray in the same direction as the wave propagation within thewaveguide.

These same techniques may likewise be employed to obtain the designparameters for reverse end-fire patterns but because a phase leadinstead of a phase lag is required, such arrays are more complex. Forthe reverse endfire arrays, the waveguide must be dielectrically loadedto lower the guide 'velocity below the free space velocity ofpropagation. This is necessary because the spacing between adjacentslots for a phase lead is large and second order beams arise from theslot positioning. By loading the waveguide with a dielectric, the guidewavelength is decreased. This in turn decreases the slot spacing2,894,261 Patented July 7, 1959 for the required phase lead to adistance which in free .space will suppress these second order beams.

Because of the required critical slot spacing, such dielectricallyloaded waveguides are extremely narrow banded and a small shift offrequency causes a large deterioration of the antenna pattern. Ininstances where the geometrical configuration of the array or theavailable space makes it impossible to move the feed point of a forwardend-fire array from one end to the other, no satisfactory broad-bandedreverse end-fire array is obtainable. Also, conical shaped antennaarrays to be broad-banded require feeding from the base of the conewhich necessitates complex distribution networks.

It is therefore an object of this invention to provide a reverseend-fire linear array which requires no dielectric loading.

It is another object of this invention to provide a reverse end-firelinear array wherein the placement of the radiating element is the sameas that of ordinary end-fire linear arrays.

It is another object of this invention to provide a new linear array ofthe reverse end-fire type.

It is another object of this invention to provide a conical array whichmay be fed from the vertex and which radiates a beam in the direction ofthe vertex.

It is still another object of this invention to provide a simplifiedbroad-banded reverse end-fire type of linear array wherein the spacingof the radiators and the relative amplitudes and phases of the drivingexcitation are substantially the same as that employed for forwardend-fire linear arrays.

In accordance with this invention an embodiment thereof may include aplurality of radiator elements, such as slots, coupled to a waveguidecapable of propagating two orthogonal linearly polarized modes. Thearray is then fed with linearly polarized waves having a plane ofpolarization perpendicular to a selected plane. The radiator elementsare, however, arranged so as to be excited only when the waveguidepropagates linearly polarized waves having a plane of polarizationparallel to the selected plane. Therefore the radiation elements are notexcited and the array behaves like an ordinary waveguide in propagatingthe wave. When the electromagnetic wave reaches the end of thewaveguide, its plane of polarization is turned through an angle ofdegrees and the rotated wave is totally reflected back into thewaveguide array. The reflected electromagnetic wave now being polarizednormal to the selected plane excites the radiator elements to produce anend-fire beam. In this manner, a reverse end-fire linear array isobtained by utilizing a reflected wave for exciting the radiators. Thespacing of the radiator elements and the driving excitation parametersare in all respects similar to the techniques heretofore employed withforward end-fire linear arrays.

Fig. l is a perspective cutaway view of a reverse endfire waveguidearray in accordance with this invention;

Fig. 2 is a perspective cutaway view of a reverse endfire antennaincluding two waveguide arrays and a suitaable feed waveguide;

Fig. 3 is a perspective view of a reverse end-fire conical antennaincluding a plurality of waveguide arrays; and

Fig. 4 is a detailed view in perspective of the feed means of theconical antenna shown in Fig. 3.

The novel features which are believed to be characteristic of theinvention, both as to its organization and method of operation, togetherwith further objects and advantages thereof, will be better understoodfrom the following description considered in connection with theaccompanying drawings, in which several embodiments of the invention areillustrated by way of example. It is to be expressly understood,however, that the drawings are for the purpose of illustration anddescription only, and are not intended as a definition of the limits ofthe invention.

Referring now to the drawings, wherein like reference charactersdesignate like parts, and particularly to Fig. 1, there is shown asquare waveguide dimensioned for propagating two orthogonal linearlypolarized wave energy modes. A selected radiating wall 12 of thewaveguide 10 includes a large number of thin, narrow, transverseradiating slots 14 excitable by polarized electric fields having a planeof polarization transverse to the radiating wall 12. The slots 14 areshown as extending transversely to the longitudinal dimension of thewaveguide 10 all the way across the waveguide 10. Such slots are usuallydesignated as nonresonant slots if its length differs from that ofone-half of a guide wavelength. Actually, the slots 14 may be of anylength but it has been found that slots extending all the way across thewaveguide are very simple to cut. Furthermore, the spacing between slotsis shown as being small (about one-twelfth of a guide wavelength) toobtain what is generally known as a leaky line. As mentioned above, thespacing of the slots, and the driving parameters determine the beamangle of the waves radiated and the slot dimension itself has been foundto contribute to the shape of the beam radiated. Consequently, when aparticular beam angle and beam cross-section is desired, the proper slotspacing and slot dimensions are selected from well known techniquesdescribed in the above-mentioned reference by Silver.

A conductive planar closure member 16 afiixed to one end of waveguide 10provides an electrical short. A conductive planar diagonal member 18extends between diagonally opposite corners of the square waveguide 10and abuts the planar closure member 16 along an edge 20 of the diagonalmember. The conductive planar diagonal member 18 extends into thewaveguide 10 a distance approximately equal to one-quarter of the guidewavelength (the wavelength of the waves within the waveguide at theoperating frequency) and its thickness is selected such as to provide amechanically rigid planar sheet.

A source 22 is connected to the square waveguide 10 to excite linearlypolarized electric fields therewithin through path 24. The arrow 26 ofFig. 1 indicates the spatial orientation of the plane of polarization ofthe linearly polarized waves excited within waveguide 10 which plane isparallel to the radiating wall 12 containing the radiating slots 14.

The operation of the reverse end-fire waveguide array of Fig. 1 is asfollows. Linearly polarized wave energy from the source 22 is propagatedalong path 24 and excites the lowest order TE-mode in waveguide 10. Theplane of polarization of these waves is parallel to wall 12 containingthe slots 14, as is shown by arrow 26 in Fig. 1. As previously stated,the radiating slots 14in the radiating wall 12 are excitable only bylinearly polarized waves having a plane of polarization orthogonal towall 12, or parallel to what will also be referred to as the selectedplane. Therefore the wave energy mode excited by the source 22 ispropagated along the waveguide without exciting slots 14 because none ofthe currents induced into the waveguide wall 12 have a componenttransverse to the direction of elongation of the slots 14.

As the linearly polarized wave approaches the combination of the planardiagonal member 18 and the planar closure member 16, a combination whichis also termed as termination means, the plane of polarization isrotated through an angle of 90 degrees into parallelism with theselected plane as defined above. This rotation is illustrated by twoarrows, the arrows 26 representing the plane of polarization prior toreaching the diagonal 18, and arrow 28 representing the plane ofpolarization after rotation. In addition to rotating the plane ofpolarization to become parallel to the selected plane, the combinationof the closure member 16 and the diagonal member 18 causes asubstantially complete reflection of the rotated linearly polarizedwave. After reflection, the rotated wave is propagated back along thewaveguide 10, i.e., in the direction of source 22. It is obvious thatthe reflection from the combination of the plate 16 and the diagonal 18is accomplished substantially without losses because no dissipativeelements are included into this termination.

The reflected linearly polarized wave having a plane of polarizationparallel to the selected plane excites the slots 14 in much the samemanner as a forward end-fire array is excited. In fact, the resultobtained is the same as if the feed array had been shifted to point 28.The excitation of the slot 14 in this manner will provide an end-firebeam which is reversed with respect to wave energy propagated from thesource 22 but is forward with respect to the direction of the reflectedelectromagnetic wave.

The term end-fire, as used herein, designates an array giving rise to abeam whose axis is either parallel to the array axis or makes an anglewith the array axis which is not degrees. An end-fire array may bedefined as an array which provides a beam which is not broadside. Inpractice, end-fire beams are those which are parallel to the array axisor make an angle therewith which is not greater than 60 degrees. Thisis, of course, arbitrary and the array of this invention may also beutilized for broad-fire beams.

It will be apparent to those skilled in the art that the teachings ofthe embodiment shown in Fig. 1 are likewise applicable to arrays whichcomprise waveguides of other than square cross-sections. For example,circular or ridge waveguides may be used in the same manner. Theimportant characteristics of all waveguides which may be utilized forthe linear array of this invention is that the waveguide can be excitedby orthogonal linearly polarized modes. Likewise, the slot radiators 14may be replaced by probes, dipoles or other well known types ofradiation elements which in combination with the array waveguide areexcitable by waves which are linearly polarized along a selected planeand which are not excited when the plane of polarization is orthogonalto the selected plane. In other words, the radiation elements must bepolarization sensitive to one of the orthogonal modes.

The reverse end-fire linear array shown in Fig. 1 and described abovemay be utilized alone, or it may be combined with similar arrays toprovide a multi-element antenna array. For instance, several arrays maybe combined to form cone shaped antennas for the nose of a high speedaircraft. As is well known, plastic radomes or nose cover units, as theyare sometimes referred to, for housing radar nose antennas becomeunsuitable when the temperatures due to atmospheric friction approachesthe blistering point of the plastic material. One solution to this heatproblem is a metallic radome comprising ordinary end-fire arrays whichprovides a forward end-fire beam. However, it has been found that thefeed distribution system to feed a number of these arrays is verycomplicated.

Fig. 2 shows a two element reverse end-fire array comprising a standardrectangular feed waveguide 30 coupled to a source 32 which excites thefeed waveguide 30 in the lowest TE-mode. The other end of the waveguide20 is coupled to the central portion of a curved waveguide section 34. Ajunction 36 formed by the rectangular waveguide 30 and the waveguidesection 34 is an H-plane T-junction for the curved waveguide section 34is of rectangular cross-section in the proximity of junction 34 andflares in width towards both ends to increase its narrow dimensions tothat of its broad dimensions. In other words, the curved waveguidesection 34 is of rectangular cross-section at its central portion and ofquare c osse i n at bot of its ends. Waveguide section 34, feedwaveguide 30 and source 32 provide a feed system.

Two substantially identical reverse end-fire linear arrays 38 and 40,similar to the array shown in Fig. 1, are coupled to the square ends ofwaveguide section 34. The arrays 38 and 40 comprise, just as explainedin connection with Fig. 1, a square waveguide which includes radiatingslots 14 in a radiating wall 12. Each array is terminated at its freeend by a closure member 16 and contains a conductive diagonal member 18in engagement with the closure member 16.

The operation of the nose array of Fig. 2 is as follows. The source 32excites the TE -rectangular waveguide mode within the feed waveguide 30.The junction 36 acts as a power divider and excites the TE -rectangularwaveguide mode in the curved waveguide section 34. The planes ofpolarization of these modes are parallel respectively to arrows 42 and42' and provide the orientation of the plane of polarization orthogonalto the selected. plane. This mode, being polarized perpendicular to theselected plane, will not excite the radiators 14 in the coupled arrays38 and 40. The mode in each array 38 or 40 is then rotated by theclosure member 16 and the diagonal member 18 in the manner previouslydescribed. In other words, the plane of polarization of the energyisrotated through 90 degrees and completely reflected. Because the planeof polarization is now parallel to the selected plane, the reflectedwaves excite the radiators 14 to provide an end-fire beam from eacharray along beam axes 44 and 44'.

Fig. 3 shows an antenna array utilizing eight reverse end-fire arrayelements of the type shown in Fig. 1 and arranged about an antenna axis50 to assume the geometrical configuration of a cone. More specifically,the waveguides define the frustum of a right circular hollow cone. Eacharray element comprises, just as the array shown in Fig. l, a squarewaveguide 10 having a plurality of transverse slots 14 in waveguide wall12. Each array is terminated, just as previously explained, by a closuremember 16 with which a conductive diagonal member 18 is in contact.

A base structure comprising an outer skin 52 and an inner skin 54 may beutilized for supporting the individual waveguides 10 in the spatialrelation shown and for providing an aerodynamically suitable structure.The outer skin 52 may be perforated by long narrow cutouts 56 to exposethe radiating slots 14 of the waveguides 10. A cylindrical waveguide 58located along the antenna axis 50 of the cone is part of the feeddistribution system and is shown in Fig. 4. A source 60 is coupled tothe cylindrical waveguide 58 and supplies the wave energy which isradiated by the slots 14.

The detailed manner in which the cylindrical waveguide 58 is coupled tothe square waveguides 10 is shown in Fig. 4. The upper end (as seen inFig. 4) of the cylindrical waveguide 58 is coupled to a radial Waveguide62. As is well known to those skilled in the art, the TE circularwaveguide mode indicated by the curved arrow 64 is electrically coupledto the TE -radial waveguide mode indicated by the arrows 66. Thewaveguides 10 are radially connected to the radial waveguide 62 whichexcites therein a linearly polarized mode, the plane of polarization ofwhich is indicated by the arrows 68 in Fig. 4.

The conical array of Figs. 3 and 4 operates as follows. Wave energy fromthe source 60 is so coupled to the cylindrical waveguide 58 as to excitethe TE -mode therewithin having electric field lines represented byarrow 64. The cylindrical waveguide 58 in turn excites the TE -radialwaveguide mode in the radial waveguide 62 which gives rise to electricfield lines represented by the arrows 66 in Fig. 4. As long as thewaveguides 10 are symmetrically spaced, an even division of wave energybetween them obtains.

The mode within the radial waveguide 62 excites the square waveguide 10by setting up a linearly polarized mode having electric vectors wheredirection is indicated by the arrow 68 in Fig. 4. Because the directionof polarization of the electric field is parallel to the walls 12containing the radiating slots 14, the currents induced into theradiating wall 12 do not have a component transverse to the direction ofelongation of the slots 14. Consequently, the slots will not be excitedand no radiation will take place.

As the linearly polarized waves are propagated through each squarewaveguide 10 they encounter the combination of the closure member 16 andthe therewith abutting diagonal 18. As explained heretofore, thiscombination rotates the plane of polarization through an angle ofdegrees and reflects the rotated waves back along the square waveguide10. Because the electric vector is now perpendicular to the wall 12 ofthe waveguides 10 containing the slots 14 electric currents are inducedinto the radiating wall 12 which have component transverse to thedirection of elongation of the radiating slots 14. The waveguides 10with the slots 14 now operate like an ordinary end-fire linear arraygiving rise to an end-fire beam in the direction of propogation of thereflected waves.

The conical array of Fig. 3 has been explained in conjunction with aradial waveguide 62. It will be emmediately apparent to those skilled inthe art that the radial waveguide serves as a distribution network forfeeding the square waveguides 10. Obviously, the radial waveguide mightbe replaced by conical waveguides or other equivalent wave distributingnetworks which excite linearly polarized waves within the squarewaveguides having an electric field parallel to the wall containing theradiating slots. It is also apparent that the radiation slots 14 aremerely shown by way of example and that equivalent radiators may besubstituted therefor.

There has been described hereinabove a reverse endfire linear arraywherein reflected wave energy is utilized for obtaining an ordinaryend-fire beam. The array usually, but not necessarily, comprises awaveguide conductor including radiation means associated therewith. Thisarray is fed by electromagnetic waves which are oriented in such a wayas not to excite the associated radiation means. In other words, theradiation means is 'disassociated from the electromagnetic waves excitedwithin the waveguide. The waves are then operated upon by completelyreversing its direction of propagation and rotating its plane ofpolarization through 90 degrees so as to completely excite the radiationmeans. There has also been described a conical array using reverseendfire linear arrays.

What is claimed is:

1. A reverse end-fire waveguide array comprising: a waveguide sectionadapted to propagate orthogonal linearly polarized electromagneticwaves, one wall of said waveguide section including radiation meansarranged to be excited by electromagnetic waves linearly polarized in afirst plane; a source of electromagnetic waves for exciting linearlypolarized waves in a second plane perpendicular to said first plane andcoupled to one end of said waveguide section; and terminal means coupledto the other end of said waveguide section for rotating the linearlypolarized waves excited by said source from parallelism with said secondplane to parallelism with said first plane and totally reflecting saidrotated waves.

2. A reverse end-fire linear array comprising: a hollow elongatedconductor of substantially uniform cross-section having a centralportion and a first and a second end portion, said conductor beingexcitable by orthogonal linearly polarized electromagnetic waves havinga plane of polarization parallel to a first and a second plane;radiation means electrically associated with said central portion forproviding an end-fire beam when said conductor is excited byelectromagnetic waves linearly polarized parallel to said first plane,said radiation means being electrically dissociated from said centralportion when said conductor is excited by electromagnetic waves linearlypolarized parallel to said second plane; a closure member electricallyterminating said first end portion; a conductive planar diagonal memberwithin said first end portion and abutting said closure member, saiddiagonal extending between diagonally opposed corners of said conductorand having a width substantially equal to onequarter of the waveguidewavelength; and source means coupled to said second end portion forexciting within said conductor electromagnetic waves linearly polarizedparallel to said second plane.

3. A reverse end-fire waveguide array comprising: a forward end-firelinear array including a waveguide and an associated radiation means,said array being excitable by electromagnetic wave energy linearlypolarized parallel to a first plane to provide an end-fire beam, saidarray propating substantially all electromagnetic waves linearlypolarized parallel to a second plane without exciting said radiationmeans, said second plane being perpendicular to said first plane; andwave reflecting means coupled to one end of said waveguide for rotatingthe plane of polarization of linearly polarized electromagnetic wavesfrom said second plane to said first plane for exciting said radiationmeans with the waves reflected therefrom.

4. A reverse end-fire linear array comprising: a waveguide sectiondimensioned for propagating orthogonal linearly polarizedelectromagnetic waves, one wall of said waveguide section includingradiation means excitable by electromagnetic waves linearly polarizedalong a first plane for radiating an end-fire beam extending in thedirection of propagation of waves linearly polarized along said firstplane; a source of electromagnetic waves linearly polarized along asecond plane perpendicular to said first plane and coupled to one end ofsaid waveguide section; a conductive closure member electricallyterminating the other end of said waveguide section; and a conductivediagonal inside said waveguide section and abutting said closure memberalong one edge thereof, the combination of said closure member and saiddiagonal turning the plane of polarization of the electromagnetic wavesfrom said second plane into said first plane and reflecting said wavestowards said radiation means.

5. A reverse end-fire waveguide slot array comprising: a squarewaveguide section, one wall of said waveguide section including aplurality of transverse, narrow, closely spaced, nonresonant slots; aconductive planar closure member electrically closing one end of saidwaveguide section; a conductive planar diagonal abutting said 010- rsure member and extending between diagonally disposed corners of saidwaveguide section, said conductive diagonal extending into saidwaveguide section a distance equal to one-quarter of a waveguidewavelength; and a source of linearly polarized electromagnetic waves coupled to the other end of said waveguide section for exciting saidwaveguide section with waves linearly polarized parallel to said wall.

6. A reverse end-fire antenna array comprising: a plurality of waveguidesections, each waveguide section dimensioned for propagating orthogonallinearly polarized modes of electromagnetic waves; a source of linearlypolarized electromagnetic waves, one end of each of said waveguidesections being coupled to said source for exciting each of saidwaveguide sections with electromagnetic waves having a plane ofpolarization orthogonal to a selected plane; radiation means includedwithin each of said waveguide sections, said radiation means beingexcitable by electromagnetic waves having a plane of polarizationparallel to said selected plane; and means coupled to the other end ofeach of said waveguide sections for rotating the plane of polarizationof the electromagnetic waves from said source to become parallel to saidselected plane and totally reflecting said rotated waves.

7. A reverse end-fire waveguide antenna comprising: a plurality ofwaveguide sections arranged symmetrically about an array axis;polarization selective radiation means associated with each of saidwaveguide sections, said radiation means radiating an end-fire beam whensaid waveguide section is excited with electromagnetic waves linearlypolarized parallel to a selected plane; a source of electromagneticwaves, a like end of each of said waveguide sections being coupled tosaid source, said source exciting each of said waveguide sections withelectromagnetic waves linearly polarized perpendicularly to saidselected plane; and terminal means coupled to the other end of each ofsaid waveguide sections, said terminal means operating upon saidlinearly polarized waves from said source by rotating the plane ofpolarization into parallelism with said selected plane and reflectingsaid rotated waves for exciting said radiation means.

8. A reverse end-fire waveguide antenna comprising: a plurality ofwaveguide sections arranged symmetrically about an array axis, eachwaveguide section dimensioned for propagating orthogonal linearlypolarized modes of electromagnetic waves; a source of linearly polarizedelectromagnetic waves, one end of each of said waveguide sectionscoupled to said source for exciting said waveguide sections withelectromagnetic waves having a plane of polarization perpendicular to aselected plane; radiation means included within each of said waveguidesections, said radiation means being excitable by electromagnetic waveshaving a plane of polarization parallel to said selected plane; aconductive planar member closing the other end of each of said waveguidesections; and a conductive planar diagonal inside each of said waveguidesections and abutting said conductive planar member, said planardiagonal having a width of one-quarter of the waveguide wavelength andextending between diagonally opposed corners of said waveguide sections.

9. A reverse end fire waveguide antenna comprising: a plurality ofwaveguide sections arranged symmetrically about an array axis;polarization selective radiation means associated with each of saidwaveguide sections, said radiation means radiating an end-fire beam whensaid waveguide section is excited with electromagnetic waves linearlypolarized parallel to a selected plane; a source of electromagneticwaves, one end of each of said waveguide sections being coupled to saidsource, said source exciting each of said waveguide sections withelectromagnetic waves linearly polarized perpendicularly to saidselected plane; a plurality of closure members each being coupled to theother end of a different one of each of said waveguide sections; and aplurality of diagonal members, each extending between diagonally opposedcorners within a difierent one of each of said waveguide sections andabutting the associated closure member, the combination of a closuremember and the associated diagonal member operating upon said linearlypolarized waves from said source by rotating the plane of polarizationinto parallelism with said selected plane and reflecting said rotatedwaves for exciting said radiation means.

10. An end-fire waveguide antenna array comprising: two square waveguidesections arranged symmetrically about an array axis; an H-planeT-junction, said waveguide sections being respectively coupled to thesymmetry arms of said junction; a source of linearly polarizedelectromagnetic waves coupled to the third arm of said junction, forexciting linearly polarized waves within said two square waveguideshaving a plane of polarization perpendicular to a selected plane;radiation slots included within a wall of each of said waveguidesections, said radiation means being excitable by electromagnetic waveshaving a plane of polarization parallel to said selected plane forradiating an end-fire beam in the direction of propagation of theexciting waves; two conductive planar members, each closing the otherend of a difierent one of said two waveguide sections; and twoconductive diagonal members each inside a ditferent one of said twowaveguide sections and abutting the associated conductive planar member,said diagonal members having a width equal to one-quarter of thewaveguide wavelength and extending between diagonally opposed corners ofthe associated waveguide sections, the combination of a closure memberand the associated diagonal member operating upon said linearlypolarized waves from said source by rotating the plane of polarizationinto parallelism with said selected plane and reflecting said rotatedwaves for exciting said radiation slots.

11. A conical waveguide antenna comprising: a plurality of squarewaveguide sections arranged about an array axis to define a hollowfrustum of a right circular cone, the outer walls of said squareWaveguides each including a plurality of thin transverse nonresonantslots arranged to radiate an end-fire beam when said square waveguidesare excited by linearly polarized waves having a plane of polarizationperpendicular to said wall; a radial waveguide for exciting within saidsquare waveguide linearly polarized electromagnetic waves having a planeof polarization perpendicular to said wall, the ends of said squarewaveguides defining the narrow portion of said cone being radiallycoupled to said radial waveguide; a cylindrical waveguide coupled tosaid radial waveguide for exciting the TE -radial waveguide modetherein; a source of electromagnetic waves coupled to said cylindricalWaveguide for exciting the TE -eircular waveguide mode therein; aplurality of conductive planar members, each closing the other end of adifferent one of said waveguide sections; and a plurality of conductiveplanar diagonal members, each inside a ditferent one of each of saidwaveguide sections and abutting the associated conductive planar member,each of said planar diagonal members having a Width of one-quarter ofthe waveguide wavelength and extending between diagonally opposedcorners of said waveguide sections, the combination of a closure memberand the associated diagonal operating upon said linearly polarized wavesfrom said radial waveguide by rotating the plane of polarization throughninety degrees and reflecting said rotated waves for exciting saidslots.

N 0 references cited.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.2,894,261 July '7, 1959 Nicholas Yarn It is herebfi certified that errorappears in the-printed specification of the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 3, line 71, for "arrows 26 read arrow 26 column 4, line 14, for"feed array" read feed of the array column 5, line 13, for "Erectangular" read TE rectangular column 6, line 19, for have component"read have a component lines 26 and 2'7, for "exmnediately" readimmediatel column '7, line 19, for "propating" read propagating P Signedand sealed this 17th day of November 1959.

(SEAL) Attest:

KARL AXLINE ROBERT c. WATSON Attesting Officer Commissioner of Patents

